Small hole electrical discharge machining method and small hole electrical discharge machining apparatus and electrode inserting method and electrode inserting apparatus

ABSTRACT

A small hole electrical discharge machining apparatus includes an electrode holder that holds an upper part of an electrode, an electrode guider that guides a lower part of the electrode, a jet nozzle that injects water jet to the electrode holder, and a fluid channel that supplies a gas, such as air, to an electrode guide of the electrode guider. The electrode is guided with the water jet toward the workpiece, such that small hole electrical discharge machining is performed while the gas is being released from the electrode guide into a working liquid via the fluid channel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a small hole electrical dischargemachining method and a small hole electrical discharge machiningapparatus, and an electrode inserting method with respect to anelectrode guide of the small hole electrical discharge machiningapparatus and an electrode inserting apparatus.

2. Description of the Related Art

In a conventional small hole electrical discharge machining apparatus, astick-shaped, or pipe-shaped, slender electrode is rotatably supportedby a main-axis portion. The main-axis portion is moved up/down by a feedscrew that is rotated by a main-axis feed motor. By doing so, a lowerend portion of the electrode is caused to come near to a workpiece andelectrical discharge is caused to occur from the electrode. Thereby, asmall hole is drilled. Then, an electrode guide member guides the lowerend portion of the electrode to a proper accurate position.

Also, conventionally, to insert the stick-shaped (or pipe-shaped)slender electrode into the electrode guide member, a water jet jettedfrom an upper part of the stick-shaped electrode enveloping the waterjet to feed the stick-shaped electrode up to the electrode guide member.

Incidentally, in the small hole electrical discharge machining that usesthe stick-shaped electrode, in order to prevent a fusion-cutting of theelectrode due to the electrical discharge, steps of the small holeelectrical discharge machining method are executed in a state where theworkpiece is placed within a working tank filled with a working liquidsuch as water or deionized water.

However, in the conventional small hole electrical discharge machiningmethod and apparatus, dirty water from a worked portion enters aninterior of the electrode guide, thereby the electrode guide got cloggedor plugged. Hence, it is difficult to perform a long-term stableelectrode feeding, and therefore continuous working was limited to oneperformed for approximately 2 hours or to one wherein the number of theworked holes was 1,000 pieces or so. Further, metal ions in the workingliquid were reduced and the resulting material accreted onto theelectrode guide. Resultantly, a hole of the electrode guide became smallin diameter, and therefore, it is difficult to perform long-term stableelectrode feeding.

Also, the conventional electrode inserting step inserting the electrodeinto the electrode guide, it is difficult to insert the electrode havinga very small diameter such as 0.01 mm, 0.02 mm, and 0.03 mm.

The present invention has been made in order to solve theabove-described problem and has an object to provide an electrodeinserting method and apparatus that make more reliable the insertion ofa very fine stick-shaped electrode into the electrode guide, and toprovide a small hole electrical discharge machining method and apparatusthat prevent entry of the dirty water, occurring within the workingliquid, into the electrode guide, as well as reduction of the metal ionsin the working and subsequent attachment of the resulting material ontothe electrode guide, to enable stable feeding of the electrode and henceenhance the working accuracy.

SUMMARY OF THE INVENTION

To attain the above object, A small hole electric discharge machiningmethod using a small hole electrical discharge machining apparatushaving electrode holding means for holding an upper part of an electrodeand electrode guide means for guiding a lower part of the electrode, theelectrode being fed to a workpiece while the electrode is being rotated,the method comprising: a supplying step supplying a gas to an electrodeguide of the electrode guide means; a releasing step releasing the gasinto a working liquid from the electrode guide; and a machining stepperforming small hole electrical discharge machining.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a small hole electrical discharge machiningapparatus according to the present invention;

FIG. 2 is a right side view of the small hole electrical dischargemachining apparatus according to the present invention;

FIG. 3 is an enlarged view of a Z-axial slide portion in FIG. 2;

FIG. 4 is an enlarged explanatory view of a IV portion in FIG. 3;

FIG. 5 is a sectional view taken along a line V—V of FIG. 4;

FIG. 6 is an enlarged explanatory view of a VI portion in FIG. 3; and

FIG. 7 is an explanatory view of an electrode inserting apparatusaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will hereafter be explained withreference to FIGS. 1 to 7.

A small hole electrical discharge machining apparatus 1 according to thepresent invention comprises a pedestal 3, a work table 5 fixing aworkpiece W and provided on the pedestal 3, and a work tank 7 providedon the work table 5 for containing the workpiece W. Also, at the rear(on the right side of FIG. 2) of the work table 5, columns 9 a and 9 bupwardly extending from the work table 5 are provided.

On the columns 9 a and 9 b, an X-axial carriage 11 that can be freelymoved and positioned in X directions (see FIG. 1) is provided. On theX-axial carriage 11, a Y-axial carriage 13 that can be freely moved andpositioned in Y directions intersecting the X directions is provided.

Referring to FIG. 3, on the front end (the left side end portion in FIG.2) of the Y-axial carriage 13, a slide base 17 is attached, and theslide base 17 is configured to freely move in vertical direction. Withrespect to this slide base 17, a Z-axial slider 19 is engaged with aguide member (not shown), and the Z-axial slider 19 is configured tofreely move in vertical direction (Z directions).

A Z-axial feed screw 21 extending in Z directions is rotatably supportedby the slide base 17. A servo motor (first motor) 23 driving androtating the Z-axial feed screw 21 is provided on an upper end portionof the Z-axial feed screw 21. Also, onto that Z-axial feed screw 21,there is screwed a nut 24 that is attached to the Z-axial slider 19.

Accordingly, by appropriately rotating and driving the Z-axial feedscrew 21 by the servo motor 23 under the control of a control device(not shown), it is possible to move the Z-axial slider 19 to a desiredposition in the Z directions.

An electrode holding means 27 equipped with a one-touch coupler 25 isrotatably provided on a lower portion of the Z-axial slider 19. Also, ahollow rotation shaft 29 upwardly extending through the Z-axial slider19 and the one-touch coupler 25 is fixed to the electrode holding means27. On an upper end portion of the rotation shaft 29, a pulley 31 suchas a timing pulley for rotating a shaft is provided. Also, the upper endof the hollow rotation shaft 29 is connected, via a rotary joint 33 anda pipeline 35, to a water supply device (not shown). Further, the pulley31 is connected, via a drive belt (not illustrated), to a drive pulley(not shown) being provided to an electrode motor (second motor) 37 forrotating an electrode.

Accordingly, the water that is supplied from the water supply device issupplied to the electrode holding means 27 by passing through a hollowportion of the hollow rotation shaft 29. Also, the electrode holdingmeans 27 is driven by the electrode motor 37.

A lower portion of the electrode holding means 27, an electrode guidemeans 41 for guiding a tip end of a stick-shaped, or pipe-shapedelectrode 39 (hereinafter, called the electrode 39) is provided. Theelectrode guide means 41 is fixed to a support plate 43 that isintegrally provided to a lower end portion of the slide base 17, by afastening member 45 such as a bolt, etc.

The electrode holding means 27, as illustrated in FIG. 4, has a collet47 that holds a tip end of the electrode 39. The collet 47 is removablyinserted into a collet holding hole 51 that is formed in a collet holder49 for holding the collet 47, and the collet holder is downwardly open.Also, this collet holding hole 51 has formed with respect thereto anaqueduct 53 that communicates with the hollow hole of the rotation shaft29.

A ring spacer 55 is inserted between an upper portion of the colletholding hole 51 and the collet 47, and the diameter of the ring spacer55 is approximately the same as diameter of the collet 47. In theinterior of the ring spacer 55, a reserve chamber 57 for storing waterthat is supplied from the aqueduct 53 is formed.

As shown in FIGS. 4 and 5, in the outer periphery of the collet 47, fouraqueduct grooves 59 communicating from the reserve chamber 57 to a tipend 47 h of the collet 47.

Incidentally, in the tip end 47 h of the collet 47, x-shaped cut grooves63 are formed. Each of cut grooves 63 reaches a chuck hole 61 of thecollet 47, and therefore the tip end 47 h can be easily elasticallydeformed. Also, on the outer periphery of a lower portion of the colletholder 49, a flange-shaped engaging portion 65 abutting a lower endportion of the one-touch coupler 25 is provided.

On the lower end portion of the collet holder 49, a collet fixing member67 for fastening the collet 47 is provided, and the collet fixing member65 is configured to engage with a tapered portion at the tip end of thecollet 47. The collet fixing portion 67 further comprises a female screw71 being screwed into a male screw 69 at the lower end portion of thecollet holder 49. By rotating the collet fixing member 67, it ispossible to perform releasing or fixing of the collet 47.

Also, the collet fixing member 67 further comprises a jet nozzle 73 thatcauses water, which downwardly flows out from the four aqueduct grooves59 of the collet 47, to be made a water jet (WJ) and injected in such amanner that it encloses, or wraps, the stick-shaped electrode 39.

On the other hand, the electrode guide means 41, as shown in FIG. 6,further comprises an electrode guide sleeve 77 having an electrode guide75 for vertically guiding, with respect to the workpiece W, the lowerend portion of the stick-shaped electrode 39 being fitted to theelectrode holding means 27.

More specifically, a lower end portion of the electrode guide sleeve 77is formed into a small-diameter portion 77 a the diameter of which issmall as compared to that of a body portion of the electrode guidesleeve 77. A ceramic-made electrode guide 75 is forcedly inserted intothe small-diameter portion 77 a, and therefore the electrode guidesleeve 77 is integrally formed with the electrode guide 75. The reasonfor inserting the electrode guide 77 a is to protect the electrode guide77 a by the electrode guide sleeve 77 that has been made of ahigh-toughness material (for example, metal).

To a support plate 43 provided on the lower end of the slide base 17,there is fixed by a fastening member (not shown) such as a bolt anelectrode holder 79 having a flange portion 78 at its upper part. In theelectrode holder 79, there is formed a fixing hole 81 for fixing theelectrode guide sleeve 77 and other parts, which is upwardly open. Inthe bottom portion of that fixing hole 81, there is formed a small hole(small-diameter fixing portion) 83 the diameter of which is smaller thanthat of the fixing or fitting hole 81.

The electrode guide sleeve 77 has a stepped portion thereof, and theelectrode guide sleeve 77 is loaded to the electrode holder 79 so as toabut the stepped portion on a bottom portion of the electrode holder 77,and the small-diameter portion 77 a projects from the small-diameterhole 83 located at the bottom portion of the electrode holder 79.

At a center-axial part of the electrode guide sleeve 77, an inner sleeve85 coaxial with the electrode guide 75 is fitted. At the center-axialpart of the inner sleeve 85, an electrode guiding hole 87 is formed, andthe diameter of the electrode guiding hole 87 is somewhat greater thanthat of the electrode guide 75. An upper end surface of the inner sleeve85 is flush with the upper surface of the electrode guide sleeve 77. Inthe upper end surface of the inner sleeve 85, a first funnel portion 89converging from upper end surface of the inner sleeve 85 toward theelectrode guiding hole 87 is formed. Additionally, chamfering isapplied, on a somewhat large scale, to the outer periphery of the upperend surface of the electrode guide sleeve 77.

On the electrode guide sleeve 77, provided a spacer 91 is provided. Inthe undersurface of the spacer 91, a countersunk hole 96 that is engagedwith the chamfered portion of the upper end surface of the electrodeguide sleeve 77 is formed. On an upper end surface of countersunk hole96, a projection portion 98 is formed protruding upwardly convex.

The spacer 91 further comprises a fixing hole 92, and a ceramic-madeelectrode guide 101 is inserted to the fixing hole 92 and fittedcoaxially with the electrode guide 75.

Incidentally, the upper electrode guide 101 is fitted into, and held by,the spacer 91 such that, when the countersunk hole 96 of the spacer 91has been brought into engagement with the chamfered portion of theelectrode guide sleeve 77, the lower end surface of the electrode guide101 abuts on the upper end surface of the inner sleeve 85.

Also, an outer ring-shaped groove 93 is formed in the outer-peripheralportion of the spacer 91. An inner ring-shaped groove 95 that is opentoward the lower end of the spacer 91 is formed with respect to aroundthe upper electrode guide 101 constructing the central part of thespacer 91. Four fluid channels 97 (a, b, c, and d) are communicatingfrom the outer ring-shaped groove 93 to the inner ring-shaped groove 95.Also, in the flange portion 78 of the electrode holder 79, a gas supplyport 103 communicating with the outer ring-shaped groove 93 is provided.

Also, in the upper part of the fitting hole 92, an open hole 94 openingto the upper part of the spacer 91 is provided.

Accordingly, a gas that has been supplied from a gas supply source (notshown) to the gas supply port 103 is supplied to the first funnelportion 89 of the inner sleeve 85 via the outer ring-shaped groove 93,fluid channel 97 (a, b, c, and d), and inner ring-shaped groove 95.

The gas that has been supplied to the first funnel portion 89 issupplied to the electrode guide 75 by way of the electrode guiding hole87 of the inner sleeve 85. Incidentally, the clearance between theelectrode 39 passing through the electrode guide 75 and this electrodeguide 75 is to an extent of 0.001 to 0.002 mm or so. Duringelectrical-discharge machining, the gas is released into the workingliquid (ordinarily an aqueduct water or deionized water) via theclearance.

On the inner surface of the fitting hole 81 of the spacer 91, a femalescrew portion is formed. A male crew of a fixing member 105 is screwedwith the female screw of the fitting hole 81. Furthermore, in theundersurface of the fixing member 105, a recess portion 100 is formed,and the recess portion 100 is configured to fit the convex portion 98 ofthe upper surface of the spacer 91.

By screwing the fixing member 105 into with the female screw portion ofthe electrode holder 79, the electrode guide sleeve 77 and the spacer 91can be press-fixed to a desired position of the fitting hole 81 of theelectrode holder 79.

In this state, the fixing member 105 is projected to the outer side ofthe fitting hole 81 of the electrode holder 79. A second funnel portion107 upwardly opening is formed on the upper part of fixing member 105.In the bottom portion of the second funnel portion 107, a small hole 109that is faced to the open hole 94 of the spacer 91 is formed.Incidentally, the diameter of each of the opening 94 and small hole 109has a size permitting the stick-shaped electrode 39 and the water of thewater jet to pass therethrough.

In a case of performing small hole electrical discharge machining by theabove-constructed small hole electrical discharge machining apparatus 1,the upper portion of the stick-shaped electrode 39 is fitted into thecollet 47 of the electrode holding means 27. Then, supply of water isperformed from the water supply device to the electrode holding means27. If doing so, the water jet (WJ) that envelopes the electrode 39 isjetted from the jet nozzle 73 after passing through the reserve chamber57 of the electrode holding means 27 and the aqueduct grooves 59 aroundthe outer periphery of the collet 47. As a result of this, thestick-shaped electrode 39 that is to an extent of 0.010 to 0.200 mm orso in thickness can be fed straight forwards from the electrode holdingmeans 27 to the electrode guide means 41 without being curved or bent bythe reactive force that occurs due to the friction between the electrode39 and the electrode guide 75.

Also, since the electrode is enveloped with the water jet (WJ), it ispossible to suppress the flexure of the electrode 39 that occurs due tothe rotation of it. This enables performing small-hole machining with ahigh accuracy.

Further, during working, a gas is supplied to the electrode guide 75 ofthe electrode guide means 27 and, while the gas is being released fromthe electrode guide 75 into the working liquid, small hole electricaldischarge machining is performed. By doing so, it results that machiningis done in such a way that the electrode 39 is supported by the gas.This enables making very low the friction resistance between theelectrode guide 75 and the electrode 39.

As the gas that is supplied to the electrode guide, there is ordinarilyused an air that is free of cost. However, other than air, it is alsopossible to use a gas such as, for example, nitrogen, hydrogen, oxygen,argon, helium, or carbon dioxide gas. Also, the temperature of the gasthat is supplied, preferably, is low and, desirably, is around 4?C. Thepressure of the gas that is supplied, desirably, is 0.05 to 1.00(kg/cm²) or so in terms of gage pressure at the gas supply port 103portion of the electrode guide means.

As stated above, by supplying a gas to the electrode guide 75 duringworking, dirty water from the portion where working is performed doesnot enter the electrode guide 75. Therefore, the electrode guide 75 doesnot get clogged. This enables performing long-term stable electrodefeeding.

Also, since the metal ions within the working liquid are prevented frombeing reduced and the resulting material is prevented from attachingonto the electrode guide, by the gas, it is possible to prevent the holeof the electrode guide from gradually becoming small. As a result ofthis, long-term stable electrode feeding has become possible.

Also, in the prior art, the distance between the electrode guide and theworkpiece needs to be 0.3 to 0.5 mm, in the present invention, thedistance can be shortened to 0.05 to 0.20 mm. And therefore, the workingaccuracy is enhanced. Specifically, whereas in the prior art, theminimum diameter of machined holes when having used an electrode whosediameter was 0.03 mm was to an extent of 0.060 mm or so, in the presentinvention, it has become possible to make the minimum diameter fallwithin the range of 0.050 to 0.052 mm.

Incidentally, in the above-described embodiment, an explanation has beengiven of an example of the small hole electrical discharge machiningapparatus, wherein the jet nozzle for producing a water jet is providedto the electrode holding means; and the stick-shaped electrode is guidedwith that water jet and, while it is being rotated simultaneouslytherewith, is fed toward the workpiece. However, there is also known theone, wherein no water jet is used to guide the stick-shaped electrode tothe electrode guide means.

For example, there is also a small hole electrical discharge machiningapparatus, wherein, between the electrode holding means and theelectrode guide means, two intermediate guiding means each for guidingthe stick-shaped electrode are disposed in such a way that the both arespaced by an appropriate distance from each other in the up-and-downdirection. These intermediate guiding means are disposed such that, whenthe electrode holder is downwardly moved, they can be horizontallyretracted in order to avoid interfering with the electrode holder.

Also, the present invention exhibits a great effect when small-holemachining is performed using an electrode the diameter of which is from0.2 mm to 0.01 mm.

FIG. 7 illustrates an example in which an electrode inserting apparatus201 usable with respect to the electrode guide is applied to theabove-described small hole electrical discharge machining apparatus 1.

The electrode inserting apparatus 201 is installed at a predeterminedposition within the work tank 7 of the small hole electrical dischargemachining apparatus 1. The “predetermined position” is a position nearthe working position in which the work piece W is machined. Theelectrode inserting apparatus 201 is desirably installed at a positionas close to the working position as possible.

The electrode inserting apparatus 201 has provided therein a vacuumaspiration head 205 attachable with/detachable from a lower part of theelectrode guide means 41. This vacuum aspiration head 205 has formedtherein a hollow-cylindrical recess portion 203 that is upwardly open.The recess portion 203 is formed such that the recess portion 203 can beengaged with a lower part of the electrode holder 79 constructing theelectrode guide means 41 in the way that the recess portion 203 isslidable with respect thereto in the Z-axial direction and hermeticallysealable with respect thereto.

Incidentally, in order to keep that lower part and recess portion 203 ina hermetically sealed state therebetween, in this embodiment, a sealmember 207 is fitted to the inside-diameter portion of the recessportion 203. However, even when, in place of using the seal member 207,setting the engagement clearance of the mutually engaged portion to beat a small value, it is possible to obtain performance capable ofresisting the practical use.

By the engagement between the recess portion 203 of the vacuumaspiration head 205 and the lower part of the electrode holder 79, asealed space 209 is formed between those elements. To exhaust the airwithin that sealed space 209, exhaust means 215 is connected, via apipeline 213, to an exhaust hole 211 formed in the bottom portion of therecess portion 203.

In this embodiment, as the exhaust means 215, there is illustrated anaspirator type vacuum aspiration device that, using an air which flowsout from an air pressure source 217 with a high speed, exhausts the airwithin the sealed space 209 via a silencer 219. Also, a vacuum pump mayalso be used.

Next, the construction of electrode penetration detecting means 221 fordetecting the penetration of the electrode through the electrode guidemeans 41 will now be explained.

In the state illustrated in FIG. 7, at the position that is on thebottom portion within the recess portion 203 of the vacuum aspirationhead 205 and that is substantially right under the electrode guide 75,there is disposed a detecting electrode 223 for detecting, by electricalconduction, that the stick-shaped electrode 39 has penetrated throughthe electrode guide means 41.

The detecting electrode 223 is connected to the minus side of adirect-current power source 227 via a lead wire 225. The plus side ofthe direct-current power source 227 is slidably connected, via a leadwire 229, to the stick-shaped electrode 39 located on the upside of theelectrode guide means 41. Accordingly, when a lower end of thestick-shaped electrode 39 is brought into contact with the detectingelectrode 223, there is formed an electric circuit in which the electriccurrent from the direct-current power source 227 flows through the leadwire 229, stick-shaped electrode 39, and lead wire 225.

Also, an electrical-conduction detector 231 is disposed in parallel withthe direct-current power source 227. The electrical-conduction detector231 is configured to detect a voltage drop due to the contact betweenthe stick-shaped electrode 39 and the detecting electrode 223 and todetect the electrical conduction.

Incidentally, regarding the electrical-conduction detector 231, it mayalso be arranged such that the detector 231 detect an electric currentflowing through the circuit as a result of the contact between thestick-shaped electrode 39 and the detecting electrode 223. Also, ifmaking the vacuum aspiration head 205 using an electrical conductor andif connection is made, via the lead wires 233 and 225, between thevacuum aspiration head 205 and the minus side of the direct-currentpower source 227, it is also possible to use the vacuum aspiration head205 itself as the substituent of the detecting electrode 223.

Hereinafter, the operation that, in the above-described small holeelectrical discharge machining apparatus 1, is performed when insertingthe stick-shaped electrode 39 into the electrode guide means 41 usingthe above-constructed electrode inserting apparatus 201 will beexplained.

First, the electrode guide means 41 is moved and positioned, byappropriately driving the X-axis and Y-axis of the slide base 17 suchthat the electrode guide means 41 provided on the slide base 17 islocated right above the electrode inserting apparatus 201.

Subsequently, by lowering the Z-axis slide 19, the electrode holder 79constructing the electrode guide means 41 is inserted into the vacuumaspiration head 205 up to a position where the lower portion of theelectrode holder 79 gets engaged with the upper portion of the vacuumaspiration head 205.

Subsequently, the electrode holding means 27 having fitted therein thestick-shaped electrode 39 is moved down while the Z-axis is beingcontrolled such that the lower end portion of the stick-shaped electrode39 is inserted into the upper electrode guide 101 constructing theelectrode guide means 41 as well as into the lower electrode guide 75.Simultaneously, on the other hand, by operating the exhaust means 215,the air within the vacuum aspiration head 205 is exhausted, thereby toaspiration-draw the stick-shaped electrode 39 and insert it into theelectrode guides 107 and 75.

As described above, through the aspiration-drawing operation of thevacuum aspiration head 205, the stick-shaped electrode 39 is fed-in fromup while it is being pulled downwards. Therefore, even when theelectrode is one whose diameter is as very small as 0.01 mm to 0.03 mmor so, it can be reliably inserted into the electrode guides 101, 75without being buckled.

Also, if the stick-shaped electrode 39 has penetrated through theelectrode guide 75, the lower end portion arrives at the detectingelectrode 223. As a result of this, the penetration through theelectrode guide 75 is detected by the electrical-conduction detector231.

If it has been detected that the stick-shaped electrode 39 haspenetrated through the electrode guide means 41, electrical-dischargeworking can be performed through moving the electrode guide means 41 tothe working position.

Incidentally, although in the insertion of the stick-shaped electrode 39into the electrode guide means 41, there is not used the technique ofguiding the electrode 39 with a water jet that envelopes the electrode39 from around the same 39, concurrently using the water jet can ofcourse be also performed.

Also, according to the present invention, since through theaspiration-drawing operation of the vacuum aspiration head thestick-shaped electrode is fed into the electrode guide while it is b ingpulled downwards, even when the electrode is one whose diameter is asvery small as 0.01 mm to 0.03 mm or so, it can be reliably inserted intowithout being buckled.

The present disclosure relates to subject matter contained in JapanesePatent Application Nos. 2002-109050, filed on Apr. 11, 2002, and2002-193235, filed on Jul. 2, 2002, the contents of both are hereinexpressly incorporated by reference in their entireties.

1. A small hole electrical discharge machining apparatus comprising: anelectrode holder that holds an upper part of an electrode; an electrodeguider that guides a lower part of the electrode; a jet nozzle thatinjects a water jet to the electrode holder; and a fluid channel thatsupplies a gas to an electrode guide, wherein the electrode guidercomprises: an electrode guide sleeve having the electrode guide at itslower end, the electrode guide sleeve extending into an electrodeholding member so that the electrode guide protrudes from a lower end ofthe electrode holding member; an inner sleeve provided within theelectrode guide sleeve and which is coaxial with the electrode guide; aspacer which holds, in the interior of the electrode holding member, anupper electrode guide to be coaxial with the electrode guide; a fluidchannel provided in the spacer and guiding a gas supplied from a gassupply port provided in the electrode holding member into an electrodeguiding hole of the inner sleeve; and a fixing member provided above thespacer and having a funnel portion for guiding the water jet into athrough hole of the upper electrode guide, and wherein the electrode isguided with the water jet toward a workpiece, and small hole electricaldischarge machining is performed while the gas is released from theelectrode guide into a working liquid via the fluid channel.
 2. A smallhole electrical discharge machining apparatus according to claim 1,wherein the gas comprises air.
 3. An electrode inserting method for asmall hole electrical discharge machining apparatus having an electrodeholder that holds an upper part of an electrode and an electrode guiderthat guides a lower part of the electrode, the electrode being fed to aworkpiece while the electrode is being rotated, the electrode insertingmethod comprising: engaging a lower part of the electrode guider with avacuum aspiration head that is removably engageable therewith; andinserting the electrode into the electrode guide guider by suction powerof the vacuum aspiration head.
 4. A small hole electrical dischargemachining apparatus comprising: an electrode holder that holds an upperpart of an electrode; an electrode guider that guides a lower part ofthe electrode; a jet nozzle that injects a water jet to the electrodeholder; a vacuum aspiration head that is detachably attached to a lowerpart of the electrode guider; an electrode insertion apparatus having anelectode penetration detector that detects that the electrode haspenetrated through the electrode guider; and a motor that rotates theelectrode guider and the electrode while small electrical dischargemachining is performed, the vacuum aspiration head comprising: a concaverecess portion which is detachably attached to the lower part of theelectrode guide guider; and an exhauster that exhausts air within asealed space that is formed by engagement between the electrode guiderand the concave recess portion, and the electrode penetration detectorfurther comprising, in the vacuum aspiration head, a detecting electrodewhich is contactable with a lower end of the electrode and anelectrical-conduction detector which is in an electric circuit formedupon contact of the detecting electrode with the lower end of theelectrode, and the electrical-conduction detector is configured todetect the electrical conduction between the electrode and the detectingelectrode, and wherein the electrode is guided with the water jet towarda workpiece, and small hole electrical discharge machining is performedwhile a gas is released from the electrode guider into a working liquidvia a fluid channel.
 5. A small hole electrical discharge machiningapparatus according to claim 4, wherein the gas comprises air.